1. Field of the Invention
The present invention relates to a light scanning device for deflecting a light beam to scan a desired surface, and more particularly to a light scanning device capable of deflecting a scanning light beam employed to scan a desired surface and a synchronizing light beam employed to produce a synchronizing signal indicative of the scanning position of the scanning light beam.
2. Description of the Prior Art
In recent years there have been developed various light scanning devices for reading out and/or recording images with a light beam. In such light scanning devices, a light beam produced by a light source is reflectively deflected by a light deflector to scan a desired object surface in a main scanning direction, while at the same time the object surface is being moved at a constant speed in a sub-scanning direction which is substantially normal to the main scanning direction. If highly accurate scanning is required in the light scanning device, then it is necessary to generate a synchronizing signal representative of the scanning position of the light beam on the object surface being scanned. One conventional way of producing a synchronizing signal has been to deflect a synchronizing light beam with the light deflector and arrange a grid with alternate bright and dark regions on the path of the synchronizing light beam so that the grid is scanned by the synchronizing light beam. The light that has passed through or been reflected by the grid is detected by a light detector, which applies a light signal to a synchronizing signal generator that converts a change in the detected amount of light to a corresponding electric pulse signal. Thus, a synchronizing signal can be generated by detecting periodic changes in the amount of light which has passed through or been reflected by the grid as it is scanned by the synchronizing light beam.
In addition to the above positional detection of the light beam in a scanning line on the object surface, it is also necessary to control the starting point of effective scanning for initiating a substantial recording or read-out cycle for each scanning line. To effect such starting point control, conventional light scanning devices have another light detector positioned on one side of the surface to be scanned. The second light detector detects the scanning light beam and generates a detection signal each time the scanning light beam traverses the light detector. Effective scanning is started in response to such a signal generated by the light detector. With the second light detector provided in addition to the grid, however, the light scanning device is complex in structure. Particularly, a light scanning device wherein sheets of different sizes are to be scanned is quite complex and highly costly to manufacture since a plurality of light detectors have to be located in positions appropriate for the different sheet sizes In order for the light detector to control the scanning starting point and for the grid to detect the scanning position, it is also necessary to put into phase a positional signal produced from the grid and a starting point signal generated by the second light detector. The procedure for fine adjustment of the positions of various components to achieve such phase equalization is however tedious and time-consuming.